I think that the twitter model of communication would work very well for disseminating information and informal discussion in the corporate world. Is there a twitter-like web-app that can be installed at the corporate level to provide this?

I think Yammer's functionality is a sort of mix between Twitter & Facebook. But I've personally found it great in helping make company internal communication more effective across different "silos" (at least in a mid-sized company with a couple of offices).
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JonikFeb 13 '11 at 20:25

Yammer is basically Twitter for Business ('yams' of information) where only employees of a company are able to access the closed environment (restricted by email domain). Discussions are possible as you can view all replys below the original message. You can follow work members and set up groups for common interests/job functions. There are now also communities:

Communities are separate Yammer networks used to
communicate with external groups,
like customers, partners, contractors,
and fans of your company.

You can have a desktop application to monitor your 'yams' in a similar way to Tweetdeck works for Twitter and there are Firefox extensions.

37 Signal has a product called backpack that is a little more than twitter but is basically what you are looking for. I believe their Basecamp product also has it built in project specific so that each project has its own feed.

+1 Using this now for internal keeping-each-other-up2date. Works nice. Although I would advice installing a plugin that mails notifications of new posts, at least in the beginning to get people noticing and get them active.
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LodeAug 22 '11 at 17:54